Deoxycytidine kinase (dCK), an enzyme in the deoxyribonucleoside salvage, is required for the phosphorylation, and thus activation, of a variety of clinically important chemotherapeutic and antiviral agents such as arabinofuranosylcytosine (araC), fludarabine, 2-chlorodeoxyadenosine (CdA), and 2'3'-dideoxycytidine (ddCyd). Clinical resistance to these compounds leads to treatment failure. Deficiency of dCK activity has been associated with resistance in a number of leukemic cell lines. However, few studies have documented aberrations in dCK in cells from patients clinically resistant to nucleoside analogs. Recently, the dCK cDNA was cloned and the gene characterized, allowing study of the molecular mechanisms of araC resistance. The tissue-specific and differentiation- specific regulation of dCK in a collected bank of leukemic cells from 52 patients with various types of leukemia will be investigated. 5- Azacytidine, a nucleoside analog that hypomethylates DNA, has been shown to induce the expression of dCK protein activity and mRNA in a dCK- deficient, araC-resistant HL60 cell line. The hypothesis is that methylation regulates dCK expression by hindering the binding of a transcription actor. The association between methylation and regulation of dCK expression will be investigated in cell lines resistant to nucleoside analogs and in the patient specimens. The major goal of this investigation is to understand the genetic mechanisms regulating deoxycytidine kinase activity. This information would lead to the development of selective pharmacologic agents aimed at circumventing cellular resistance and enhancing selective cytotoxicity to nucleoside analogs used in treating cancer and viral infections. Lanier Ayscue, the candidate for this application, has a demonstrated history of achievement in research with 10 publications, a poster presentation at a national meeting and 7 abstracts. Dr. Ayscue received two competitive research fellowships, one during medical school and the other during residency training. In addition to her research activities, she graduated with Honors from the UNC School of Medicine and was inducted into the Alpha Omega Alpha Honor Society. The sponsor of this grant, Dr. Beverly Mitchell, is one of the leading researchers in purine and pyrimidine metabolism in whose laboratory the deoxycytidine kinase gene was cloned. Dr. Ayscue's career in academic medicine will be greatly enhanced by the opportunity to continue her research on dCK gene expression in an environment enriched by seminars sponsored by the Lineberger Comprehensive Cancer Center, the Curriculum in Genetics and the Departments of Medicine and Pathology at the University of North Carolina at Chapel Hill.